1. Field of the Invention
This invention relates generally to ink jet recording apparatus for recording letters and/or pictures on a recording medium by an ink-discharge using an airflow, and which responds to an electric signal, and particularly to an ink jet recording apparatus with pressure adjustable mechanisms for discharging a constant ink amount.
2. Prior Art
Recently, various types of printers are popularly utilized as peripheral equipment. Above all, ink jet printers have advantages such as noiselessness, ease of application to color printers, and high picture quality. As to methods for discharging ink, the use of an airflow and an electrostatic force bring about a superior response. Various types of ink jet printers are known, and one example of the ink jet printers is disclosed in U.S. Pat. No. 4,403,234.
A conventional ink jet recording apparatus using an airflow and an electrostatic force comprises a nonconductive air nozzle plate having an air nozzle and a conductive ink nozzle plate being set in parallel with the air nozzle plate. The air nozzle plate has an electrode and has an ink nozzle for keeping an ink meniscus. The electrode and the conductive ink nozzle plate are connected to a signal source to establish an electric field gradient therebetween. The ink nozzle plate and the air nozzle plate are secured to a rear housing to define an ink chamber and an annular airflow chamber. The ink chamber is connected to an ink tank for storing ink therein through an ink pipe, and the ink receives a constant pressure by a pressure regulator regulating a pressurized air from the air supply source. The pressurized air from an air supply source flows into the annular airflow chamber via an air pipe, and then flows out via the air nozzle. Such airstream makes a sharp pressure gradient at an annular laminar-airflow space between the ink nozzle and the air nozzle. Owing to the electric field gradient and the sharp pressure gradient, the meniscus is extended and discharged via the air nozzle.
A condition of the meniscus is influenced by a difference between the level of the ink in the ink tank and the level of the ink nozzle, and by a distance between the air nozzle plate and the ink nozzle plate. The difference and the distance give great influence to recording characteristics including a record response of ink jet printing head and a threshold voltage, i.e. the minimum voltage for ink-discharge. Therefore, the difference and the distance have to be set to an optimum value such that an ink meniscus formed at the ink nozzle is in a convex shape.
However, if the distance has an error of only 2 or 3 .mu.m, the difference has to be change by approximately 20 to 30 mm indeed to make the meniscus having the convex shape, so that an adjustment amount of the difference comes to large. Thus, there is a problem relative to the adjustment of the difference. In addition, if such conventional mechanism for adjusting the difference is applied to a multi-head printer, the deference does not assume a constant value, or varies among ink jet heads, due to difficulty in practical manufacturing processes.
To remove the above problems, a mechanism for moving the ink tank up and down is considered. However, this technique has another drawback that it is required another mechanism for moving the ink tank in response to the amount of remaining ink, thereby complicating the structure of printers.